The present invention relates to a new halogen-free composite film, a process for its manufacture, and its use as a flexible, multi-purpose material.
In recent years, the demand for halogen-free films and halogen-free laminated films has grown tremendously on account of expanding environmental awareness and increasingly stringent legal requirements. The use of halogen-free films averts the production of toxic reaction products during temperature build-up in the event of fire. The materials that were primarily used hitherto, such as polyvinyl chloride compounds, no longer satisfy these requirements. In addition, laminated films should also satisfy requirements for high temperature resistance, low shrinkage, and excellent chemical resistance, especially excellent hydrolytic resistance. Moreover, these laminated films should be simple and fast to produce so that they satisfy commercial requirements.
The disadvantages of the known films that are used for the manufacture of ribbon cables are that they are not flexible enough, they are too heavy, and above all are not adequately temperature resistant. They tend to delaminate at high temperatures. Many films are insufficiently chemical resistant and also have low tensile strength. When the known films are used for ribbon cable, the inserted stranded wire can corrode in certain applications if it is not protected adequately.
Thus for example, from DE 42 00 311 A1 is known an adhesive-free ribbon cable of noncrystalline or semicrystalline thermoplastic that is manufactured by hot pressing of thermoplastic strips and metallic conductors. Although these ribbon conductors have good thermal loading capacity and a long service life, they have the disadvantage that they are relatively stiff and consequently very susceptible to breakage. A further disadvantage of these ribbon cables is the slow production speed so that economically advantageous manufacture is not possible. Many of the polymers mentioned have low adhesion to copper, and thus do not have good sealing characteristics to this metal, so they are not suitable for many applications. Moreover, two monofilms are used here, which fuse completely in the press at high temperatures and slow manufacturing speeds, and thus are extremely difficult to process in a laminating station.
DE 42 39 982 A1 describes a ribbon cable that is lightweight, does not corrode, and has excellent electrical conductivity. The cable comprises a plurality of electrical conductors consisting of layered graphite, which are arranged such that they extend parallel to one another and are encased in an electrically insulating material made of a synthetic resin. These ribbon cables cannot be used at high service temperatures, and hence do not have the necessary temperature stability. Due to the use of halogen-containing compounds to improve the electrical conductivity in conjunction with polyvinyl chloride as a synthetic resin material, there is a risk of these cables forming halogen-containing decomposition products in the event of a fire. Moreover, these halogen-containing ribbon cables are subject to shrinkage, with the result that they no longer satisfy modern requirements. In addition, hydrolysis problems can occur with these ribbon cables, so these cables cannot be used in motor vehicle applications.
DE-OS 27 44 998 describes a flat conductor ribbon cable in which a number of band-shaped conductors that run parallel to one another and spaced apart are adhesively joined to a film of insulating material by an interposed adhesive layer, wherein the spaces between the conductors are covered with an opaque layer that is resistant to ultraviolet radiation. However, these ribbon cables cannot be used in applications in which the conductor""s permeability to light is important. Moreover, no quality inspection of the manufactured cables can be performed during and after production.
DE 196 32 153 A1 relates to the use of a plastic mixture for halogen-free cables with polypropylene and/or its copolymers as a basis, which additionally contains magnesium hydroxide. In order to achieve the necessary abrasion resistance and the mechanical characteristics without impairing the required flame resistance, ethylene vinyl acetate and/or its copolymers and the magnesium hydroxide are added in surface-modified form. As a result of the addition of ethylene vinyl acetate, the flame resistant properties are improved through a synergistic effect with magnesium hydroxide. However, a disadvantage of using the above described combination is that these ribbon cables have insufficient temperature resistance and their mechanical and chemical properties are inadequate. Particularly in the automotive field, polyolefin materials cannot be used because of their low flame resistance, modest flow properties and poor dimensional stability.
None of the known films simultaneously fulfills the requirements for good hydrolytic resistance, excellent mechanical and chemical resistance, use at high long-term service temperatures, good flame-resistant properties, and that they be halogen-free.
Consequently, the object of the invention is to prepare a halogen-free composite film and a process for manufacturing the same, wherein the composite film must satisfy the above-mentioned requirements.
This object is achieved in that the halogen-free composite film in accordance with the invention includes at least one to N sealable, multi-layered laminated films, wherein N is an integer from 2 to 10. A functional layer and/or a functional element is interposed between the individual laminated films. The individual sealable, multi-layered laminated films are composed of a first and a second film that are bonded together by means of a laminating adhesive or lacquer. The films in the individual laminated films can be identical to and/or different from one another.
The functional layer and/or the functional element can be a printed circuit board, a sensor, a metallic stranded wire or a metallic conductor material or an electronic component, wherein the material for the metallic stranded wire or the conductor material is selected from the group consisting of copper, silver, iron, nickel, aluminum, or an alloy of these metals.
The composite film manufactured in accordance with the invention can be used at high long-term service temperatures, has good mechanical resistance, in particular high tensile strength and elongation at break, is resistant to hydrolysis, flame-resistant, and resistant to chemicals, and additionally has low shrinkage.
The process for manufacture of the composite film in accordance with the invention is characterized in that a laminating adhesive or lacquer is applied to the first film of each laminated film, the film thus coated is dried in a drying tunnel at temperatures from 80xc2x0 C. to 180xc2x0 C., preferably 100xc2x0 C. to 120xc2x0 C., a second film is supplied at the end of the drying tunnel and joined to the first film, then this laminated film is reeled up and the laminating adhesive is finally cured, then a functional layer and/or a functional element is placed between this first laminated film and a second laminated film that was produced in the same manner, and the first laminated film is laminated to the second laminated film.
If the sealing characteristics of the laminated film are not adequate in view of the later application, the side of the laminated film facing the incoming second film is customarily provided with a thermally activated substance. This thermally activated substance achieves the result that the sealing characteristics of the composite film are improved.
Films from the group consisting of LCP (liquid crystal polymer), PPS (polyphenylene sulfide), PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PK (polyketone), PEK (polyetherketone), PEEK (polyetheretherketone), PEKK (polyetherketoneketone), PEEKK (polyetheretherketoneketone), PEI (polyetherimide), PESU (polyether sulfone), PSU (polysulfone), COC (cyclo-olefin copolymer), and polyamide films may be selected as the first and/or second film.
Especially suitable as laminating adhesive or lacquer are adhesives of the type normally made of acrylates, polyurethanes, polyester urethanes, epoxides, copolyesters or natural adhesive resins. These adhesives can be used as single-component or multi-component systems. They may be products that can be used as aqueous dispersions, as solvent-containing systems, or solvent-free systems. Mentioned by way of example here are products in the ADCOTE line from the Rohm and Haas company, which are single-component and multi-component adhesives with good thermal resistance and excellent resistance to chemicals.
The following can be used as thermally activated substances, depending on the later use of the composite film: copolyester systems, cyclo-olefin copolymers, polyurethanes, acrylates and derivatives thereof, vinyl acetate copolymers, polyvinyl alcohols, polyvinyl butyrals, polyvinyl acetates, sealable maleic resins, alkyd resins, polyolefins and polyamides. In addition, saturated, unsaturated, linear and/or branched copolyesters can also be used, such as products from the DYNAPOL line from Degussa. These materials are distinguished by the fact that they are durable yet at the same time are intrinsically flexible, bond well to metals, and have good resistance to chemicals.
Furthermore, solvent-containing multi-component polyurethane primer systems can be used, such as products from the Pentacoll line from Rohm and Haas. This combination of thermally activated substances with a primer is advantageous when extremely high composite strength is required.
The individual laminated films are bonded as described above with a functional layer and/or a functional element into a laminate, in a laminating station, making a composite film for further use. In this context, the individual laminated films can have the same structure, or, depending on the application, can consist of different first and second films and contain different laminating adhesives.
The composite film is suitable as a protective or cover film in the manufacture of flexible printed conductors.
In addition, the composite film in accordance with the invention can be used as a cover film for printed circuit boards. When the composite film is used in the area near an engine, EMC shielding is possible. The ribbon cables manufactured with the laminated film can also be used for industrial white goods.
Moreover, the composite film can be used to manufacture flexible ribbon cables that are used at high service temperatures such as those that occur in applications in the engine area, especially in the automotive field, in airbag technology, for interior wiring in motor vehicles, in motor vehicle headliners, in the engine compartment and in headlights. Especially in the engine compartment and for headlights, long-term service temperatures in excess of 140xc2x0 C. are necessary; the composite film in accordance with the invention can be used in this application without difficulty.
Any materials that conduct electric current can be used as metallic conductors for the manufacture of ribbon cables. Metals that can be considered include all the customary conductor metals, such as copper, silver, iron, nickel, aluminum, or alloys of these metals. The metals to be processed can be up to 200 xcexcm in thickness.
Moreover, the composite film can be used as a protective film and/or cover film for flexible printed conductors.